Driving mechanism for the type bed of cylinder printing machines



Jan. 29, 1957 A. BUTTNER DRIVING MECHANISM FOR THE TYPE BED 0F CYLINDER PRINTING MACHINES 6 Sheets-Sheet 1 Filed Oct. 17. 1955 II f.

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DRIVING MECHANISM FOR THE TYPE BED 0F CYLINDER PRINTING MACHINES Filed 001;. 17. 1955 6 Sheets-Sheet 2 Jan. 29, 1957 A. BUTTNEJR 2,779,198

Jan. 29, 1957 A. BUTTNER DRIVING MECHANISM FOR THE TYPE BED OF CYLINDER PRINTING MACHINES 20 25 i? H i1: 7: 12 Mg,

Jan. 29, 1957' A. BUTTNER 2,779,198

DRIVING MECHANISM FOR THE TYPE BED OF CYLINDER PRINTING MACHINES Filed Oct. 17'. 1955 6 Sheets-Sheet 4 Jan. 29, 1957 Filed Oct. 17. 1955 6 Sheets-Sheet 5 8b 12 13 x a a 15 16 3g j 6 j 20 19a 6 1957 A. BUTTNER DRIVING MECHANISM FOR THE TYPE BED 0F CYLINDER PRINTING MACHINES 6 Sheets-Sheet 6 Filed Oct. 17. 1955 United States A, Patent DRIVING MECHANISM FOR THE TYPE BED OF CYLINDER PRINTING MACHINES Artur Biittner, Heidelberg, Germany, assignor to Schnellpressenfabrik Aktiengesellschaft Heidelberg, Heidelberg, Germany, a corporation of Germany Application October 17, 1955, Serial No. 540,978

Claims priority, application Germany October 26, 1954 5 Claims. (Cl. 74-27) This invention concerns driving mechanism for producing reciprocating movement of the type bed of a cylinder printing machine. In contrast to known driving mechanisms of this kind, which are suitable only for stop-cylinder machines or for cylinder machines having a constantly rotating impression cylinder, the type bed driving mechanism of the present invention is applicable in its basic structure to all types of cylinder printing machines.

In comparison with known mechanisms of this kind, the invention is distinguished in that it retains in principle the proved advantages of the rolling-off gear wheel-crank drive, also called the rolling wheel-crank drive, without possessing its disadvantages. The transmission members for the type bed driving mechanism may be arranged both in the center of the machine and at the sides. In both cases, a casing may be provided for the driving mechanism to protect it from dirt, which is not possible, for example, with the rolling wheel drive of the prior art, which is open in the center of the machine.

For convenience of and to provide for the possibility of subsequent repairs, it is preferable to arrange the principal transmission members laterally outside the framework of the machine. Moreover, with such an arrangement, a complete covering of the principal driving parts becomes possible, so that they are able to run in an oil bath.

The type bed driving mechanism proposed by the present invention is further applicable to any kind of drive in which the back and forth movement of the type bed is efiected by means of a shaft which undergoes an alternate clockwise and counterclockwise rotation. In contrast to many known type bed driving mechanisms of this kind, all the driving parts of the mechanism of the invention remain in constant positive connection, an advantage which, in the case of cylinder printing machines having a constantly rotating impression cylinder, contributes to the smooth running of the machine.

According to the present invention a type bed drive for cylinder printing machines includes a toothed segment, a gear wheel engaged with and adapted to be rolled along said toothed segment, whereby said gear wheel is caused to execute an oscillating motion about a fixed axle, at least one toothed rack secured to the type bed, there being in engagement with said rolling gear wheel, a further gear wheel mounted to rotate on said fixed axle and adapted directly or indirectly to transmit the motion of the first gear wheel to said toothed rack.

The oscillating motion of the rolling gear wheel may be produced by a regularly or irregularly rotating crank assembly. In the latter case the type bed is moved with approximately uniform speed during the printing process :and more rapidly on the return stroke.

The oscillating motion of the rolling gear wheel may be produced by a regularly or irregularly rotating crank assembly. In the latter case the type bed is moved 2 with approximately uniform speed during the printing process and more rapidly on the return stroke.

The toothed segment may be mounted rigidly 0n the framework of the machine, which is suitable for stopcylinder machines and oscillating cylinder machines. According to a further feature ,of the invention, however, it may also be mounted so that it oscillates round the axis of oscillation of the rolling wheel, and, for the complete compensation of the irregularity of the movement of the type bed which is still present during the printing operation, it may be caused to oscillate by means of a cam driving mechanism. This form of construction is specially suitable for cylinder printing machines having a constantly rotating impression cylinder. In such a construction, the toothed segment is carried, for ex ample, by two roller levers, which maintain positive control by means of two cam discs. In this way a second correcting movement is forcibly applied to the oscillating gear wheel While it is rolling along the toothed segment. This form of construction makes it possible to impart a completely uniform or linear movement to the type bed during the greater part of the distance traversed during the printing operation, which movement coincides with that of the uniformly rotating impression cylinder. A type bed driving mechanism constructed in such a. way is suitable for single and two revolution machines, in which the impression cylinder rotates uniformly.

This latter form of construction represents an improvement of the type bed driving mechanism shown in German Patent No. 576,178 or U. S. Patent No. 2,066,- 429.

The invention will be described further, by reference to the accompanying drawings, wherein all the known devices of a cylinder printing machine which are not necessary for an understanding of the invention are omitted, and in which:

Fig. 1 is a side elevation of a part of a cylinder printing machine together with the driving members for reciprocating movement of the type bed constructed in accordance with the invention and with the cover of the driving mechanism removed. In this mechanism the movement of the type bed is effected according to the crank diagram, so that one half of the complete revolution of the crank is utilized for the printing operation and one half for the return stroke of the type bed. The printing operation and the return stroke take place nonlinearly as is customary with stop-cylinder and oscillating cylinder printing machines.

Fig. 2 is a cross-section taken on the line AA of Fig. 1 and viewed in the direction of the arrows, showing the type bed driving mechanism arranged in the center of the machine.

Fig. 3 is a sectional view taken on the line AA of Fig. 1, but with the type bed driving mechanism attached.

Fig. 4 is a horizontal section taken on the line BB of Fig. 1, and viewed in the direction of the arrows.

Fig. 5 is a side elevation similar to Fig. 1 of a second type of construction of cylinder machines. In this embodiment, however, a lagging crankgear is introduced into the crank drive. This lagging crankdrive requires, for example, an angle of rotation of 210 in order to rotate the crankshaft through 180 for the printing operation, while the remaining angle of rotation of causes the subsequent half revolution of the crankshaft and with it the return stroke of the type bed in a correspondingly shorter time. The printing operation thereby takes place approximately linearly.

Fig. 6 is a horizontal section taken on the line CC of Fig. 5, and viewed in the direction indicated by the arrows. This section is differentiated from that of Fig-4 by the lagging crank drive of Fig. 5, which is connected to the crankshaft. The essential driving members for the production of the reciprocating movement of the type bed are retained unaltered.

Fig. 7 is a side elevation similar to that of Fig. 5, of a third type of construction of a cylinder printing machine. In this embodiment the oscillating gear wheel does not roll along a fixed segment, but the segment is internally toothed likewise to receive an oscillating motion. By this means the course of movement during the printing operation is so far transformed that the movement of the type bed takes place substantially linearly. This driving mechanism is suitable for machines having a constantly rotating impression cylinder, such as single and two revolution machines.

Fig. 8 is a horizontal section taken on the line D D of Fig. 7. This view is distinguished from that of Pig. 6' in that the driving members for the oscillating movement of the internally geared segment are illustrated.

Fig. 9 is a cross-section of the machine taken on the line EE of 7, and viewed in the direction of the arrows.

Fig. shows the speed-time curve of the type bed driving mechanism of Pig. 1 for the normal crankshaft drive.

Fig. 11 shows the speed-time curve of the type bed driving mechanism of Fig. 5. By the introduction of the lagging crank-gear, the driving of the type 'bed takes place with a lengthened time for the printing operation at an approximately linear running speed, while the return stroke takes place more quickly; and

Fig. 12 shows the speed-time curve of the type bed driving mechanism of Fig. 7. By means of the additional control of the internally-geared segment during the rolling off of the gear Wheel during the printing operation, the speed of running of the type bed is made substantially linear, as is required by cylinder machines having a constantly rotating impression cylinder.

In the embodiments of the invention shown in the drawings, wherein similar reference numerals are employed throughout the various figures to denote similar parts, 1 represents the type bed, which carries a flat form 2. During its back and forth movement over the distance s, the type bed passes under the form inking rollers 3 which ink the form, and the printing operation then takes place under the impression cylinder 4, only a portion of which is diagrammatically illustrated. The movement of the type bed takes place on several roller tracks 5, whereby the stresses which arise are taken up by the base framework 6 of the machine. In the first embodiment of the invention as shown in Fig. 2, a toothed rack 7 is situated below the type bed in the center of the machine and engages with a gear wheel 8. A short axle 9, on which the gear wheel 8 is rigidly mounted, is rotatably journalled at both sides in flanged bushings 10 and 11'. Levers 12 and 13 are rotatably mounted on the hubs of the two flanged bushings and are connected by means of a bolt 14 to jointly support a gear wheel 15, which is rotatably mounted on the bolt- 14. The oscillating movement around the axle 9 is effected by a connecting rod 16, which is connected with the levers 12 and 13 by means of the bolt 14. The oscillating motion of the gear wheel 15 is derived from a crank pin 17 on the crank wheel 18. During the oscillation of the bolt 14 about the length of path b indicated in Fig. 1, the gear wheel 15 is rolled along an internally-toothed segmental element 19, which is tightly screwed to the base frame-6. The length of the path over-Which the wheel 15' rolls on the segment 19, as also the motion about the central wheel 8, givesthe tot-a1 length of the path s traversed by the type bed 1, which is transmitted through the central wheel 8 to the rack 7.

The embodiment shown in Figs. 3 and 4 having driving mechanism attached, uses essentially the same driving mechanism as that of Big, 2. According to Eigs, 3 and 4, flanged .hushingslO nd: 1a a ffiae to heouter. walls he. b se. r me. n av iournall d. herein a haft 9a which is driven in alternate directions of rotation. Gear wheels 8a and 8b are also fixed on the shaft 9a inside the walls of the base frame 6. These gear wheels 8a and 8b are also fixed on the shaft 9a inside the walls of the base frame 6. These gear wheels 8a and 8b engage with toothed racks 7a and 7b, which are fastened on both sides of the type bed 1. The gear wheels 8a and 8b project upwards through integrally cast slotted holes 6a formed in the base frame 6. One end of the shaft 9a is provided with a projecting pin 92: which is supported in a flanged bushing 2E. The flanged bushing 21 is fixed in a cover 20 adapted to enclose the driving mechanism, as shown in Fig. 3, and which is fastened to the base frame 6. Cover 20 may be screwed on so that it is oil-tight, and consequently the driving members can operate in an oil hath. For convenience, it is important that the driving mechanism be able to operate While completely open, without the cover 2&3, so that satisfactory adjustment and control of the driving members is possible. With further reference to Fig. 4, it may be noted in addition that the crank pin 17 is supported in the driving mechanism cover 20 by means of a return crank 22 provided with a bearing pin 23. The crank wheel 18 is fixed on a shaft 24, which is rotatably mounted at both sides in the base frame 6. During a back and forth movement of the type bed 1, the crank Wheel 18 performs one revolution. A pinion 25, which is rigidly connected with the driving shaft 26, engages with the crank wheel 18, the driving shaft being rotatably mounted in the base frame 6. Rigidly connected with the driving shaft 26 is a V-belt pulley 27, which through the V-belt 28 transmits the drive from the motor, which is not shown. A hand wheel 29 is also mounted on the shaft 26 externally of the base frame 6.

The embodiments shown in Figs. 1 to 4 relate to type bed driving mechanisms which operate with the normal crank drive and Whose course of movement is carried out according to the curve shown in Fig. 10. The periods for the printing operation and the return movement are 180 in each case and the running speed of the type bed takes place irregularly approximately sinusoidally. The respective type bed speeds, which are denoted by V, are given on the ordinates and the time 2, in period of 30, on the abscissae. The period during which the form is under the impression cylinder is given as a small hatched section in a portion of the speed curve.

The embodiment of type bed driving mechanism shown in Figs. 5 and 6 is distinguished from the previously described in that the crank assembly is driven with a varying angular velocity by means of the introduction of a lagging crank drive. This comprises uniformly rotating twin wheels: 18a and 18b mounted eccentrically relative to the bearing pin of the crankshaft 24 by an amount indicated by the reference letter x.

A lagging crank 30 is rigidly connected with the crankshaft 24 and is also connected with the uniformly rotating twin wheels 18a and 1812 through a guide rod 31 by means of a pin 32 and a pin 33. The twin wheels 18a and 1811 are driven by means of pinions 25a and 25b, which fit tightly on the driving shaft 26. The crankshaft 24 is set into similar rotation by means of the guide rod 31, but does not rotate uniformly, but with a variable angular velocity. The crankshaft performs a retarded half revolution during the printing operation and, as shown by Fig. 11, over a time period of 210,while the return stroke of the type bed is performed over a time period of The twin wheels 18a and 18b: rotate about two bearings 34 and35, the diameters of which are so dimensioned that the bearings of thecrankshaft 24 lie inside the bearings of the twin wheels 18a and 18b. The twin Wheels 18a and 18b are bolted together by means of several spacing pins 36, 36a and 36b (Fig. 5). The crankshaft 24 is journalled at 24b in a cover 37 (Fig. 6), which is screwedon tothe baseframe 6 in an oilrtight manner. The Whole lagging crankdrive is dis posed inside the machine in a box-like casing cast integrally with the base frame 6. The crankshaft 24, 24a and 24b may form one piece with the crank pin 17 of the outer crank web 22 and bearing pin 23. All the remaining members of the driving mechanism correspond to the members shown and indicated in Figs. 1 to 4.

In Figs. 7 to 9 there is shown an embodiment of type bed driving mechanism which is suitable for machines having an impression cylinder rotating constantly in one direction, such, for example, as single or two revolution machines.

In this embodiment, the movement of the type bed takes place according to the speed curve shown in Fig. 12. The diiference relative to the curve of Fig. 11 consists in that the movement of the type bed during the printing operation takes place absolutely linearly. The period of the printing operation is prolonged to 210 as in Fig. 11, while the return stroke is carried out more quickly, in a period of 150. These conditions are therefore the same because, for the construction according to Figs. 7 to 10, the same lagging crank drive is connected to the crankshaft as in the case of Figs. and 6. The only new driving members added in the embodiment of Figs. 7 to are control members for an additional oscillating movement of the internally toothed segmental element 19. During the rolling motion of the gear wheel 15 in the toothed segment 19, this toothed segment 19 is rotated about the axle 9 in such a way that an additional rotation of the gear wheel 15 results, which correspondingly corrects the motion of the type bed. The irregularity, which is still present during the printing operation in the curve shown in Fig. 11, is transformed by the additional oscillating movement of the segment 19 into an absolutely linear speed over the greater part of the length of the path of the type bed. During the return stroke of the type bed, no additional control of the segment 19 takes place. All the remaining members of the driving mechanism therefore correspond exactly to those which are shown in Figs. 5 and 6. The same reference numerals have consequently once again been used for these parts.

The newly added control members for the additional oscillating movement of the segment 19 consist of two roller levers 38 and 39, which are rotatably mounted on the shaft 9a. The levers 38 and 39 are of flanged construction, whereby they are tightly connected with one another through the toothed segment 19, by bolts 40, 40a and 40b.

A bifurcation 38a is formed on the roller lever 38, and together with the bolt 41, forms a bearing for a roller 42. The roller lever 39 also has a bifurcation 39a and carries a bolt 43 supporting a roller 44. A cam disc 45 is attached to the web 22 of the crank shaft 24 and a cam disc 46 to the web 24a. The cam disc 46 is of exactly complementary shape to the cam disc 45, so that during the rotation of the crankshaft 24 together with the cam discs attached to the webs 24a and 22, the roller levers 38 and 39 between them maintain a continuous movement. The two roller levers, coupled together and with the segmental member 19a placed between them, form a rocker arm which swings about the shaft 9a. The stroke of the rollers 42 and 44 is denoted by the reference letter y. The cam discs 45 and 46 lie outside the frame 6 of the machine and are easily fitted during assembly in such a manner as to ensure absolute synchronism of the type bed with the circumference of the impression cylinder. The gears for the rotation of the impression cylinder are not shown, since clearly the arrangement thereof can be effected in any conveniently known manner.

The method of operation of the type bed driving mechanism for cylinder printing machines shown in Figures 1 to 4 is as follows:

The pinion shaft 26, driven in a known way, transmits its rotation through the pinion 25 to the crank wheel 18. This crank wheel carries out one revolution during one forward and return movement of the type bed 1. On the crank wheel 18 is secured the crank pin 17, which moves with it the connecting rod 16 mounted on the pin 17. The other, bifurcated end of the connecting rod 16 is connected with the oscillating levers 12 and13 by the bolt 14. During one revolution of the crank wheel 13, the bolt 14 is therefore swung back and forth over the distance 12 indicated in Fig. 1. The gear wheel 15, which is mounted on the bolt 14 and which rolls along on the fixed internally toothed segment 19 during the oscillating movement, participates in this oscillating movement. The rotation of the gear wheel 15 thus produced is transmitted to the gear wheel 8 with which it is engaged and which is rigidly connected with the shaft 9 or 9a. The shaft 9 or 9a is consequently set into an alternating clockwise and counterclockwise rotation. By means of the engagement of the teeth of the type bed toothed racks 7 or 7a and 7b, the alternating rotary movement of the shaft 9 or 9a respectively is converted into a straight-line r..- ciprocating movement of the type bed. The type bed is consequently moved along from the position in front of the inking rollers, as shown in Fig. 1, through the distance .9 up to the reversing position behind the impression cylinder 4.

It is of no significance for the course of the movement whether the transmission to the type bed takes place as shown in Fig. 2 only by way of a toothed rack in the middle of the type bed, or, as shown, for example, in Fig. 3 and in the subsequent figures, with toothed racks arranged to the left and right of the type bed. The latter construction, in addition to the gear wheel 8 on the shaft 911, requires two further gear wheels to rigidly connected with the axle and to engage with the toothed racks on the type bed.

It is, of course, also possible, in the case of a lateral arrangement of the driving members as shown in Fig. 3, to arrange only one gear wheel in the middle of the type bed instead of two gear wheels 8a and 8b, as shown, for example, in Fig. 2. These differences of arrangement have in themselves no effect on the method of operation.

In an embodiment of type bed driving mechanism as shown in Fig. 1, the course of movement of the type bed for the periods of the printing operations and the return movement takes'place according to the speed-time curve of Fig. 10. The movement takes place approximately sinusoidally and the period occupied by the printing operation is equal to that required for the return movement. Thus, half a revolution of the crank wheel is required for the printing operation, and also for the return movement.

Cylinder machines with this kind of type bed move ment are suitable for stop-cylinder and oscillating-cylinder printing machines.

The method of operation of the embodiment of type bed mechanism for cylinder machines shown in Figs. 5 and 6 differs from that of the previously described construction only in that the crankshaft carries out its rotation with varying angular velocity; this therefore has the effect, because the lagging crank drive shown is connected to the main crank drive, that for half a revolution of the crankshaft during the printing operation, an angle of rotation of 210 of the lagging crank drive is needed, while the second half revolution of the crankshaft during the return stroke of the type bed is carried out more rapidly, namely in an angle of rotation of the lagging crank driving wheels 18a and 18b of only Thus, as shown by the speed-time curve of Fig. 11, the period occupied by the printing operation is prolonged from to 210 and the period of the return stroke is shortened to 150. The speed-time curve now shows that during the printing operation the type bed is consequently moved with approximately linear speed; the great irregularity of the movement produced by the normal crank curve, as shown in Fig. 10, is thus removed.

As shown in and previously described with reference to Figs. 5 and 6, the rotation is transmitted to the twin wheels 18a and 18b by way of the driving shaft 26 together with the pinions 25a and 25b. The bolt 33, on which the guide rod 31 is mounted, is fixed in the two twin wheels, the other end of the guide rod 31 being connected by means of pin 32 with the lagging crank 30, which is itself affixed on the crankshaft 24. While the wheels 18a and 1811, which are mounted eccentrically relative to the crankshaft by the given amount x, are uniformly rotated, the crankshaft is set in a rotation having a varying angular velocity due to the connection of the guide rod with the lagging crank. The eccentric displacement, as well as the radii of the pins 32 and 33 and the length of the guide rod 31, are so proportioned in the embodiment illustrated that the uniformly rotating twin wheel 18a and 18b must pass through a sector angle of 210 in order to turn the pivot 17a of the crankshaft through 180. The printing operation accordingly takes place approximately linearly, as the curve of Fig. 11 also shows, while the return stroke takes place more rapidly, during a rotation of the twin wheels 18a and 13b of only 150.

This kind of type bed movement is also used for stopcylinder and oscillating-cylinder machines, and is additionally employed in cylinder machines wherein the impression cylinder rotates continuously in one direction, said rotation however, being carried out not uniformly but in exact agreement with the speed of the type bed during the printing period.

The third embodiment of the invention deals with a type bed driving mechanism for cylinder machines which operate with the impression cylinders rotating uniformly in one direction, i. e. the so-called single or two revolution machines.

As shown in Figs. 7 and 8, the same lagging crank driving mechanism is connected to the crankshaft as previously described, with reference to Figs. and 6. In the construction of Figs. 7, 8 and 9, however, there are also included the driving members for the additional oscillation of the internally toothed segment 19a. The toothed segment 19a is not tightly bolted to the base frame 6 as in the first two embodiments, but is fixed as a traverse between the two roller levers 38 and 39. These roller levers are mounted to be freely pivotable on the axle 9a. Both roller levers have bifurcated ends 38a and 39a and carry rotatably mounted rollers 42 and 44. The upper arm of the roller lever 38 runs with its roller on the cam disc 45, which is attached laterally to the crank web 22. The lower arm 39 runs with its roller on the cam disc 46, which is similarly bolted to the crank web 24a. On rotation of the crankshaft, the rotation of the gear wheel in alternate directions and the movement of the lagging crank drive are as previously described, and this description need not here be repeated. During the rotation of the crankshaft as shown in Fig. 7, the roller levers 38 and 39 are compelled to oscillate to and fro by the amount y. The internally toothed segment 19a also participates in this oscillating movement. This additional oscillation takes place while the type bed is moved in the direction where the printing operation is effected. The gear wheel 15, by means of the additional oscillating movement of the toothed segment 19a receives an additional correcting movement which is transmitted in such a way that the irregularity in the course of the movement during the printing operation according to an Fig. 11, which is still present, is changed into an absolutely linear movement, as shown in Fig. 12.

As can be seen from the small hatched section which indicates the actual printing operation in the curve of Fig. 12, said printing operation in this embodiment is effected with absolute regularity. This regularity corresponds to the peripheral speed of the impression cylinder, which can be determined in accordance with the speedtime curve.

The type bed driving mechanism proposed by the invention can, of course, also be constructed by using an externally toothed segment instead of the internally toothed segment 19 or 19a which has been illustrated. It is also possible to effect gearing up or down of the rolling Wheels by introducing differences in diameter between said wheels and the gear wheels which engage with the type bed toothed racks.

The type bed driving mechanism of the present invention is also applicable to cylinder printing machines in which the type beds are moved, not in a horizontal, but in a vertical direction.

What I claim and desire to secure by Letters Patent is:

1. Type bed driving mechanim for a cylinder printing press having a frame and a reciprocating type bed, comprising at least one rack fixed to the type bed and extending longitudinally thereof, a first gear wheel rotatably supported by said frame with its axis disposed transversely of said bed, driving connections between said gear wheel and rack, an arcuate internal gear segment concentric with said axis and radially spaced from said first gear wheel, a second gear wheel meshing with said first gear wheel and with said gear segment, means supporting said second gear wheel for rotation about its own axis and for oscillation bodily about the axis of said first gear and means for producing bodily oscillation of said second gear wheel about the axis of said first gear wheel, the resulting rotation of said second gear wheel as it rolls along said gear segment being transmitted through said first gear wheel to produce reciprocation of said bed.

2. Mechanism according to claim 1, in which the means for producing oscillation of said second gear comprises an asymmetric crank assembly providing lower speed of oscillation during the printing stroke of the type bed and a higher speed on the return stroke.

3. Mechanism according to claim 2, in which means is provided for oscillating said gear segment in predetermined relationship to the oscillation of said second gear to produce uniform speed of movement of the type bed during the printing operation.

4. Mechanism according to claim 3, in which said means for oscillating said gear segment comprises a cam and cam follower.

5. Mechanism according to claim 3, in which said means for oscillating said gear segment comprises two cam discs of complimentary shape and two cam rollers carried by arms connected to said gear segment, said rollers engaging said cams and providing positive movement of said gear segment in opposite directions.

References Cited in the file of this patent UNITED STATES PATENTS 

